Basic Wellbore Validation

Transcription

1 Basic Wellbore Validation Nov 2016

2 Document History & Control Version Date Author Oct 2016 Steve Hawtin Nov 2016 Steve Hawtin Crown copyright 2016 You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence, visit gov.uk/doc/open-government-licence/ or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or Any enquiries regarding this publication should be sent to us at Oil & Gas Authority Limited.

3 1 Introduction One of the responsibilities of the Oil and Gas Authority (OGA) is to provide accurate and trusted data about the UK s oil industry related activities. A key element of that commitment is to ensure that a reliable list of wells and their characteristics is available. For a variety of historical reasons the data that the OGA currently holds about wellbores is inadequate. There are missing values and inconsistent attributes that mean the data fails to achieve the minimal standards required to be of value to the OGA and its customers. In order to address this issue the OGA has undertaken a project to drive immediate improvement in the quality of its wellbore data collection. This document is in three parts: first there is an outline of the minimal data standards; next it lists the quality checks that the OGA will carry out; and finally it describes a tool to identify quality issues and make it easier for companies to submit corrected values. Figure 1: Wellbore attribute quality issues (for all offshore wells) The responsibility for maintaining and reporting data about wellbores rests with the original licensees and their successors. So where there are data quality issues the corrected values must be supplied by these companies. In order to smooth this process the OGA has constructed a spreadsheet based tool that shows the data the OGA holds and where it fails to achieve the listed minimal quality standards. The tool will be supplied to each responsible company pre-populated with the wellbores that the OGA has assigned to them. Chapter 4 in this document (page 24) gives an introduction to the tool and explains how it can be used. By manipulating values in this tool the licensee is able to address identified data issues. When this review and correction work is completed the results can be dispatched back to the OGA who will apply the proposed corrections. It is the OGA s intention to create a comprehensive data standard for wellbore data at some future time. It is expected that this will require input from industry and will result in a detailed wellbore data standard. However, since the task of creating a complete standard will take some time it was felt that a focused project to bring the existing data to a bare minimal standard was the most immediate priority. When the full standard is published it is expected that the OGA will approach the responsible companies to obtain the values of additional wellbore attributes. 1

4 1.1 Contents 1 Introduction Contents Assistance, advice, queries or suggestions Minimal Wellbore Data Intrinsic Attributes Mandatory Attributes Optional Attributes Quality Tests Wellbore Validation Tool The Overall Process Control Tab Wellbores Tab Original Data Tab Rules Tab Expect Attributes Tab Constants Tab Tests and Summary Tabs Reference List Tabs Assistance, advice, queries or suggestions The OGA has invested effort to make it as easy as possible for companies to participate in this data quality initiative. There are, however, still liable to be issues that are not adequately addressed in this short document. If you have any questions, suggestions or comments about this document, the data fixing tool or any other aspect of this project please send them to: Steve Hawtin steve.hawtin@ogauthority.co.uk +44 (0) Sharon Matthew sharon.matthew@ogauthority.co.uk +44 (0) Andy Thompson andrew.thompson@ogauthority.co.uk +44 (0) Phil Harrison phil.harrison@ogauthority.co.uk +44 (0)

5 2 Minimal Wellbore Data In order for any set of data to be worth employing it must achieve a certain minimal level of quality. If it fails to do so then the lack of trust placed in the data dramatically reduces the impact it can have. The list of wellbores held by the OGA is an important component in decisions taken both within The Authority and externally. It is not uncommon for those that utilise the OGA data to raise concerns about its quality. These comments are often rooted in particular anecdotes, where an attempt to draw conclusions has been frustrated by missing values or apparent inconsistencies. Individual instances are important, but to sustain improvement in data quality a more systematic approach has to be applied. In other words it is hard to measure data quality unless you first define and document at least some kind of minimal standard that data can be diagnostically compared against. A comprehensive data standard would document a number of aspects: The business justification for gathering and sustaining the data The key activities that employ the data, exploring which components have most impact The people and roles that create, manipulate or consume the data A description of the systems of record that hold the definitive versions of data, as well as an indication of the key systems that consume it or contribute to it The data structure, including reference values and conventions A systematic list of mandatory and indicative quality rules to be applied (preferably in both a widely understood form and in one or more formally implementable constructs) A register of the key related categories of data that have dependencies, or that deliver dependencies A list of those involved with defining, approving and updating the data standard An outline of the way standards for the data are to be updated as business needs evolve At some future date the OGA will, in consultation with industry, create this type of more comprehensive data standard for wellbores. However, in the meantime, the wellbore data held by OGA needs immediate improvement. This document is an intermediate definition that contains some of these components and explains the minimal standard that wellbore data should achieve in the short term. This chapter focuses on the structure of wellbore data; that is the attributes and reference values. The attributes of a wellbore have been divided into three groups: Intrinsic: the attributes that identify a particular wellbore such as the well number Mandatory: attributes that are required and must adhere to certain conventions Optional: additional attributes that may be supplied at the discretion of those responsible This chapter mirrors those three topics, each of which has its own section. There are some general points that are worth making about the attributes. Where there are distances specified it is to be assumed that the units of measure are metres. This simplifies the definition of the wellbore structure since it removes the requirement to define specific units of measurement for every 3

6 length based attribute. If values need to be converted from feet (where no specific type of foot is indicated) it should be assumed that International Feet are intended, that is that one foot is exactly m. In the UK sector there are few occasions when text values require accented characters or unusual symbols. Therefore, unless explicitly allowed, most text values should be confined to the 7bit ASCII character set unless specific steps are taken to explain why this is inadequate. 2.1 Intrinsic Attributes These attributes are those employed in order to ensure that the wellbore is unambiguously defined. The value of these attributes has been supplied by OGA and, in most cases, it is expected that any issues with them will be addressed by OGA. The one obvious exception is the RESPONSIBLE_COMPANY field; in this case there may be a dispute about which company should supply the information. This can be indicated by modifying this attribute in the relevant wellbores (in column B ). Of course if the company feels that any of these intrinsic values should be corrected they can signify this by editing it. The intrinsic attributes applied here are: WELLREGNO Wellbore Registration Number RESPONSIBLE_COMPANY Responsible Company Group COUNTRYCOD Legislative Area QUADRANTNO Quadrant BLOCKNO Block Number BLOCKSUFFI Block Suffix PLATFORM Platform Letter DRILLSEQNO Drilling Sequence Number WELLSUFFIX Well Suffix DENNO DEN Number (internal OGA use) Wellbore Registration Number The Identifier The OGA well Registration number must be quoted in full on all returns well logs, reports and correspondence. PON 1 12 defines the registration number as consisting of: Country: one character code to define the regulatory authority covering the well Quadrant: the number, or letter, of the quadrant in which the well is drilled. UK quadrants are areas enclosed by one degree of latitude and longitude Block: the number of the block within the quadrant in which the well is drilled Block Suffix: a single lower case letter indicating which licence block the well was within Platform: offshore platform, subsea cluster designation or land site 2 Drilling Sequence: the well s drilling sequence number as assigned by the OGA Well Suffix: a single capital letter that indicates when the wellbore is a respud or sidetrack 1 Petroleum Operating Notices define specific requirements and reporting obligations for UK Exploration and Production activities 2 PON 12 states that the platform component of the OGA registration number either contains a single upper case alphabetic character or a blank. The naming convention actually employed by OGA uses a space when there is no platform letter present. 4

7 These components of the name also appear as independent attributes within the wellbore, this use will be outlined in more detail below. One might assume that combining the current values of these attributes of a wellbore would deliver the identifier; unfortunately this is not quite correct. For a number of historical reasons these intrinsic attributes have been modified (to reflect changes or to correct anomalies) after the well name was selected. Here are some examples of valid well names: 97/12-1: The first well drilled in the 97/12 block 15/27-5: The fifth well drilled in the 15/27 block 15/27-5Z: The first side-track on the 15/27-5 well 15/26a- 6: The sixth well drilled in the 15/26 block, which happens to have been drilled within the a licence sub-block 15/26a- 6A: The first respud of the 15/26a-6 well 15/26b-W1: The first well drilled from the W platform, which happens to be in the 15/26b licence sub-block L97/10-10: The tenth well in the 97/10 block (an on-shore well) L97/10-A1: The first well drilled from the land based A platform in block 97/10 LO/06-6: An onshore well drilled in the O quadrant (which happens to be in the onshore licence block SK62a ) LO/06-5: An onshore well drilled in the same O/06 block but in a completely different onshore licence block (in this case the onshore licence block SK52a ) M112/19-1: An offshore well drilled in the 112 quadrant but within the Isle of Man s territorial waters Well Aliases There are a few occasions where a well has been aliased. For example if an exploration well is subsequently hooked up to a platform it can end up with two distinct well registration numbers. Figure 2: Three stages in the development of the Saxon field An example of this occurs in one of the wells in the Saxon field. It was originally drilled as a sidetrack of the 21/23b-7 well. The S platform was placed on top of this well and the 21/23b-S1 well was drilled. When the 21/23b-7 sidetrack was attached to the platform it was given the alias of 21/23b-S2. Subsequently two further sidetracks were drilled and assigned the names 21/23b-S2Z and 21/23b-S2Y. If aliases are ignored one might expect the wellbore 21/23b-S2 to exist (given that the 5

8 S2Z well is a sidetrack of it), however all its well data is maintained under the 21/23b-7Z wellbore. This single well origin has some wellbores numbered in sequence by the block and some by the platform so it has the potential to deliver false positives on Rule Responsible Company This attribute defined the company group that are responsible for the well. PON9 states that Obligations towards the OGA for Licence Data are borne jointly and severally by all companies who are party to a licence and not by the Operator of that licence alone therefore responsibility for the well rests with the company that originally drilled the well, its partners and successors. The obligation to maintain the wellbore data is imposed in perpetuity (in practice it remains until the OGA acknowledges in writing that all the necessary data has been delivered to a suitable repository, for example to the NHDA). Given this wide ranging responsibility it may seem counterintuitive to assign responsibility to a single company group. In practice however it is usually obvious who the lead partner has been for a particular well over the course of its lifecycle and that single organisation will usually hold the most trustworthy records. In cases where the lead partner is no longer able to deliver the data (for example the company has ceased trading) then the OGA will pursue the other partners to fulfil these obligations Country This wellbore attribute is a single character code used to define the regulatory regime under which the well was drilled. It can take on the following values: <Blank>: An empty value indicates that this is an offshore well L : This indicates that the well was drilled onshore M : Indicates wells drilled under the jurisdiction of the Isle of Man This could easily be confused with the more common definition of the word, which would be a nation recognised by the United Nations. All the wells listed belong to the United Kingdom, but this is not what this attribute indicates. 6

9 2.1.4 Quadrant Figure 3: UK Quadrants are employed for naming wells The quadrant containing the well, this has either a quadrant number (from 1 to 449) or a single upper case letter (from A to Y ). The way quadrants have been assigned means that there is a complex relationship between the quadrant s identifier and the area it indicates. In addition (as section discusses) the exact definition of the quadrant s corner locations depends on the relevant geodesy Block Figure 4: Each quadrant is divided into 30 blocks This attribute holds the number of the block containing the well. The block number is a two digit number from 01 to 30. This subdivision of the quadrant is employed to name wells that are both onshore and offshore. 7

10 There are two other distinct elements that are also commonly referred to as blocks. When dealing with onshore locations the Ordnance Survey grid is divided into 10km squares that are often referred to as blocks, in this context these are called OS Blocks. The other place where the word is used is to refer to licenced blocks (which are often subdivisions of blocks or OS blocks). Where these variants are used they have been tagged Block Suffix A block suffix is a single lower case letter used to indicate that the block has been subdivided. When part of a licence is initially relinquished the retained part is assigned the suffix a, subsequent relicencing may create licenced sub-blocks indicated by the letters b, c and so on. The licence block suffix may, or may not, form part of the OGA well number. If, for example, a well was drilled before the block was sub-divided then its name may omit the block suffix (even if the wellbore has the Block Suffix attribute set) Platform If the well was drilled from a platform then this is indicated with a single upper case letter Drilling Sequence Number The Drilling Sequence Number (DSN) is the consecutive chronological number of the well within the block or from the platform, consisting of digits with no leading zero. When this document was written no drilling sequence number required more than two digits. The chronological sequence number is allocated to the well only after it has commenced drilling to a specific bottom-hole target location, as follows: exploration, appraisal or single satellite subsea development wells will normally be numbered at the time a well is spudded i.e. when drilling commences from surface wells forming part of a multi-well development, in which casings are batch set prior to finalising the slot/target allocation, will be numbered only after drilling has commenced to a specific target location, normally at the time of drilling out of the 20, or equivalent, surface casing shoe Any proposed well that has not yet started drilling should have a blank sequence number. This presents a potential problem when identifying the well since its name will appear to be invalid. It should be noted that the Drilling Sequence Number is quite distinct from the Wellbore Sequence Number and the two should not be confused. The drilling sequence number is an integer; the wellbore sequence number should be in the form of WB1, WB2 and so on Well Suffix The well suffix is a single capital letter that distinguishes different related wellbores. There are three reasons for adding a well suffix letter: Re-spud: If a well is re-spudded for any reason, it is distinguished by an upper case character A, B, C, etc. 8

11 Sidetrack: If a well is sidetracked and the abandoned part of the hole has significant data (i.e. logs, MWD and/or core), the sidetrack is distinguished by Z, Y, X, etc. Redrill: the letter R is employed to indicate that a well has been redrilled, this should therefore never appear as a suffix on the well number In PON 12 it is suggested that platform wells cannot have respuds, however this seems to contradict the data. When a sidetrack is for strictly mechanical reasons and the abandoned part of the hole does not have significant data (i.e. logs, MWD and/or core) and is not through any known hydrocarbon bearing interval the suffix is supposed to be not required. However, again the existing data values seem to contradict this DEN Number This is an internal code employed by the OGA to manage hardcopy data about off-shore wells and should not require any input from the company. 2.2 Mandatory Attributes Having employed the intrinsic attributes to identify the wellbore the following attributes provide a minimal set: WELL_ORIGIN Well Origin WELLBORE_SEQUENCE Wellbore Sequence Number FIELD Field Name TOPHOLEDTM Top Hole Coordinate Reference System TOPHOLEYDD Top Hole Latitude TOPHOLEXDD Top Hole Longitude BOTHOLEDTM Bottom Hole Coordinate Reference System BOTHOLEYDD Bottom Hole Latitude BOTHOLEXDD Bottom Hole Longitude DATUMELEV Elevation of the well datum (in m) DATUMTYPE Well datum type GROUNDELEV Ground height above sea level (for on-shore wells) WATERDEPTH Depth of water (for offshore wells) TOTALMDDRI Total measured depth (from well datum) TVDSSDRILL Total vertical depth (from sea level) ORIGINAL_LICENCE The full original licence designation LICENCE_TYPE The type of the original licence OPERATOR The name of the current operating company (for active wells) ORIGINTENT The original purpose of the well SPUDDATE The date the wellbore was started DATETDREAC The date the deepest extent was reached COMPLEDATE The date the wellbore was completed COMPLESTAT The current status of the wellbore FLOWCLASS The types of liquid present VERIFICATION_COMPANY The name of the company that last validated the data VERIFICATION_DATE The date when the data was validated 9

12 2.2.1 Well Origin Figure 5: A single well can combine multiple wellbores 3 The entities being discussed here are actually wellbores, some of which are related to each other through sharing a common origin at the surface. This attribute defines the name of the wellbore that provides the surface location of this one. For wells with no respuds or sidetracks the well origin name and the well registration number will be the same. If the wellbore is a sidetrack the well origin should be the name of the initial wellbore that shares a surface location, for example the well called 110/02b-R3 has a well origin of 110/02b-R3 while 110/02b-R3Z shares an origin and hence also has a well origin value of 110/02b-R3. When a further sidetrack to 110/02b-R3Z was drilled (called 110/02b-R3Y ) its well origin was also 110/02b-R3. In the UK this is made harder to track because the wellbore name may be changed for certain sidetracks. One example of this is the well 9/13-A7; this well was completed in 1977 and was a producer. In 1993 the well 9/13-A54 was drilled as a sidetrack of the 9/13-A7 well. Because 9/13-A7 had a production history and yet had ceased production this new wellbore was assigned a new drilling sequence number. Again in 2013 another sidetrack was drilled, this time it was assigned the number 9/13a-A85. The insertion of the additional a indicates that by this time the original licence had been subdivided. This type of process (where a sidetrack is drilled to regain production from a previously producing well) is called slot recovery. Generally the operation will involve abandonment (to AB1, see page 17) of the donor wellbore at some point above the reservoir, as deep as possible to avoid redrilling the overburden, but providing a sufficient angle to reach the new target. In the case of A54, the kick off point was at 3346 feet ( m) so there is a lot of the original A7 wellbore still in use by A54 and A85. 3 This diagram is from the PPDM What is a Well document available from 10

13 The well origin is not accessible using the current set of OGA data, so this has been deduced from the CDA data. There are three types of cases: Any OGA wellbore that is apparently absent from the CDA data has been assigned its own name as the well origin Where the well origin noted in CDA appears absent from the OGA wellbores a reasonable wellbore has been assigned. This occurs in six cases 110/13a-E1, 206/08-3, 211/26-10Z, 22/11-5R01, 48/17a- 11 (which seems to be a misspelling for 48/17a-E1) and 9/13b- 25 Where the well origin in CDA matches a well in OGA that has been used Figure 6: Wellbores cannot have well origins that are not the primary wellbore The intention is that the well origin is the initial well at the given surface location, in other words only wellbores with wellbore sequence numbers of WB1 can act as well origins. To reiterate the target wellbore for the well origin property must always have itself as its own well origin Wellbore Sequence Number The wellbore sequence is another element from the PPDM system. This provides a numeric indicator of which wellbore this is within a single well origin. The wellbore sequence numbers are of the form WB1, WB2 and so on. Figure 7: Multiple wellbores sharing the same origin 11

14 The example shown schematically in Figure 7 above, shows the ten wellbores that all originated in the 11B slot of the A platform in block 16/26. In this case there were four different phases of production: 16/26-A17 staring in 1996; 16/26-A35 starting in 2000; 16/26-A57 starting in 2006; and finally 16/26-A59 starting in Field This attribute defines the name of the field primarily associated with a particular well. If there is no recognised field then this may be the special string NOT IN FIELD. The spreadsheet provides a list of the OGA recognised field names in the _FIELDS tab. This attribute should be selected from that list. If this constraint is too restrictive then the list may be extended through discussion with OGA. There is an active project to define a system of records for OGA fields. This may impact the field attribute of wellbores Licence Type This indicates the licence type under which the well was drilled. For offshore wells there is just one type of licence: P : A production licence For land wells there is a longer list of licence types: AL : Appraisal Licence CE : DL : Development Licence EXL : Originally a new type of Exploration Licence (from the 1984 act) these have now all been converted to apply the same terms as PEDL ML : Mining Licence old style licence from the 1950s PEDL : Petroleum Exploration and Production Licence Original Licence This attribute provides the licence number under which the well was drilled. For offshore wells the licence number will always be P followed by an integer, the integer value will be at least 3 digits long, padded with leading zeros if necessary. In the CDA data this attribute is called the Licence Number ; this should not be confused with the numeric part of the licence number, so a valid value for this attribute would be something like P456 rather than the bare number Coordinate Reference Systems (Geodetic Datum) TOPHOLEDTM Top Hole Coordinate Reference System BOTHOLEDTM Bottom Hole Coordinate Reference System The surface hole and bottom hole positions each have a geodetic datum attribute that specifies how to interpret the location. It is important that one of the permitted reference datums is specified and that all calculations employ the appropriate operations. 12

15 Figure 8: Selecting which geodetic datum to use There are three Coordinate Reference Systems employed in the UK oil industry: ED 50: for offshore positions East of the Thunderer Line ETRS89: for offshore positions West of the Thunderer Line OSGB 1936: for positions that are onshore The Thunderer Line is a dividing line running North/ South at 6 W (in ED 50). The European Survey Petroleum Group (EPSG) defines the following codes for these three CRS s: 4230: geographic 2D ED : geographic 2D - ETRS : geographic 2D - OSGB 1936 Most GPS systems report their position in the WGS84 datum. For practical purposes this is identical to the ETRS89 datum that is used west of the Thunderer line. Any datum shift that has to be applied should employ the Common Offshore transformation, that is the full 7 parameter shift defined in EPSG (with the Coordinate Transformation codes 1311, 1314 and 1315) rather than one of the simpler 3 or 4 parameter shifts Original surface position TOPHOLEYDD Top Hole Latitude TOPHOLEXDD Top Hole Longitude The position at the surface is defined in terms of the longitude and latitude (in the selected Geodetic Datum). This is expressed as a pair of real numbers (that is not using degrees minutes and seconds). 13

16 It is common practice (although not strictly correct) to enter a single platform location as the top hole position for wells drilled from the same platform. It is important that any wellbores where this approach is adopted specify a valid Slot Number so that their well origins can be verified Bottom Hole Position BOTHOLEYDD Bottom Hole Latitude BOTHOLEXDD Bottom Hole Longitude The position of the bottom hole is defined in terms of the longitude and latitude (in the selected Geodetic Datum). This is expressed as a pair of real numbers (that is not using degrees minutes and seconds). It is possible (but fairly unlikely) that the bottom hole location could employ a different reference system from the top hole location. Rule 16 checks for this (but delivers a note rather than an error) Well Datum Type Figure 9: Types of Well Datum There are a restricted set of datum types that should be employed: RT: Rotary Table KB: Kelly Bushing GLE: Ground Level Elevation (for on-shore wells) Note that strictly speaking all on-shore wells should have both a GROUND ELEVATION value and a well datum (for example the height of the Rotary Table or Kelly Bushing). However wells that only provide an elevation above sea level will be allowed (providing the value makes sense in relation to the other parameters). Previous communications from DECC have suggested that Mean Sea Level (MSL) could also be considered a valid well datum. This can no longer be accepted as the distance from Mean Sea Level to Mean Sea Level should always be 0 (and hence provides no information about the well at all). 14

17 Well Datum This is the distance from a defined point to Mean Sea Level. Negative values indicate a datum below Mean Sea Level. Measurements recorded in the wellbore are referenced from this point Water Depth/ Ground Elevation GROUNDELEV Ground height above sea level (for on-shore wells) WATERDEPTH Depth of water (for offshore wells) This is the distance from mean sea level to either the seabed (for water depth) or ground level. In both cases the normal direction is positive, that is water depth is positive downwards and ground level positive upwards. In addition to knowing the height of the well datum from mean sea level there are occasions when it is valuable to understand the elevation of the ground (for onshore wells) or the depth of water (for offshore wells). Since each well can either be onshore (with a Ground Elevation) or offshore (with a Water Depth) these two values should never both be set. The attribute that is inappropriate should have a blank value (never a 0). In some quadrants the depth of the sea floor or height of the land surface are fairly uniform. For example in Quadrant 48 the seabed is between 10m and 55m below the surface, if a wellbore in this quadrant claims to have a water depth of 107.9m it is reasonable to assume that there has been confusion about units of measure and to return to the original records to check Driller s TD Figure 10: Measured Depth is from well datum, Vertical Depth is from mean sea level The total depth of the well according to the driller, measured from the well datum as a distance along the wellbore ( MD ) TVDSS driller Another key piece of information about the wellbore is the depth that the well was drilled to as a true vertical depth from sea level (TVDSS). 15

18 There is a point that is worth emphasising here. This parameter is the true vertical depth sub-sea; the previous parameter (drillers TD) was the measured depth from the well datum. That means that the following inequality must always be true: TVDSS <= Drillers TD - Well Datum It is common for there to be confusion between TVDSS and, for example TVDKB Spud Date This is the date on which the well was first spudded. It may have a blank value for any well that is planned but has not yet started drilling Date TD Reached This is the date on which the total depth was reached. It may only have a blank value for a well that is still currently drilling or where drilling has not yet started Completion date This is the date on which the drilling was completed. The date a well is left in one of three mechanical states following drilling: Completed for Production - the date that perforation and setting of tubing and packers is finished and the well is ready to produce Abandoned - the date that the well bore, on completion of operations, is left in such a condition that the open hole is plugged and sealed such that it may not be re-entered (in general this will involve the cutting and retrieval of casing strings, removal of all drilling mud and similar fluids, and permanent sealing of the wellhead with no components remaining at surface) Suspended (temporarily abandoned) - the day that the casing above the mud line is severed following the setting of cement plugs. Figure 11: The length of time between spud date and completion date for UK off-shore wells There are a number of ways in which this date can obviously be seen to be incorrect. If it occurs before the spud date, for example, however there are many wells whose dates seem unlikely without being, strictly speaking, impossible. As Figure 11, above, illustrates the majority of wells in the North 16

19 Sea are completed within 60 days of the Spud date. When a completion date is more than a year after the spud date it is not necessarily incorrect, but it does hint that it should be checked Current Operator If a well is not currently being operated it is acceptable to leave this attribute blank. Where a well s status is not abandoned then the operating company should be assigned a valid company name Original Well Intent The original intent of the well, this is specified with a single letter code: A : Appraisal E : Exploration D : Development Completion status The completion status of the well can be one of: PLANNED : A well that has been planned but not yet started drilling DRILLING : A well that is being drilled at the moment AB1 : The reservoir has been permanently isolated AB2 : All intermediate zones with flow potential have been permanently isolated AB3 : The well origin at surface is removed. The well will never be used or re-entered again COMPLETED_OPERATING : Completed well that is currently active COMPLETED_SHUT_IN : Completed well that is shut in PLUGGED : A well that has been temporarily plugged Abandoned Phase 1 requires that permanent barrier material is placed to fully isolate all reservoir producing or injecting zones from the wellbore. The tubing may be left in place, partly or fully retrieved. Abandoned Phase 2 states that all intermediate zones with flow potential have been permanently isolated. This may require the tubing to be partly retrieved if still present. Isolating liners, milling and/or retrieving casing and setting cement or permanent barrier material to isolate intermediate zones, with flow potential from each other and communication within the wellbore. The phase is complete when no further permanent barriers are required. An Abandoned Phase 3 occurs when the well is fully abandoned and the wellhead and conductor have been removed. At this point the well will be removed from the well examination scheme. Phase 3 may include installing near-surface cement if required. Because the code AB3 indicates that the wellhead has been removed it must apply to all the wellbores associated with a single well origin. If one wellbore is AB3 then they must all be, conversely if one wellbore is not AB3 then none of them can be. In the names of the states COMPLETED_OPERATING and COMPLETED_SHUT_IN the word COMPLETED is not strictly necessary since any well that is either shut in or operating must have 17

20 been completed. However these values have been inherited from other sources and so the longer form will continue to be employed to maintain compatibility Flow Class The flow class specifies the fluids associated with the well: CWGS: Condensate, water and gas shows CWOS: Condensate, water and oil shows DH: Dry Hole GCS: Gas and condensate shows GCW: Gas, condensate and water GOCW: Gas, oil, condensate and water GOW: Gas, oil and water GS: Gas shows GW: Gas and water GWOS: Gas water and oil shows HI: Hydrocarbon indicators OCW: Oil, condensate and water OGS: Oil and gas shows OS: Oil Shows OSCS: Oil shows and condensate shows OW: Oil and water OWCS: Oil, water and condensate shows OWGS: Oil water and gas shows UNKW: Unknown, the value has been searched for but cannot be found Verification Company This attribute lists the company that verified the CDA values. The name here is the CDA company name so cannot be verified against either the OGA company list or the OGA company group list Verification Date This is the date that the wellbore data was verified on within the CDA system. 18

21 2.3 Optional Attributes In addition to the mandatory attributes there are a number of optional ones that may also be populated. NAME The well name DEVTYPE The development type of the well SLOTNO The slot employed (if it is a platform well) PARENTROLE The role within the parent wellbore PRIMARYTAR A code for the primary target OTHERCLASS A well designation supplied for historical reasons Wellbore Name In addition to the OGA identifier there may be other names under which the wellbore is known. This is a free text name so cannot be verified. It is most commonly employed for on-shore wells providing the name of a nearby town or village to help identify the well Development Well Type The DEVTYPE attribute indicates the type of development the well was intended for, for example Producer, Injector or Disposal Slot Number A free text description providing an identifier of the slot within the platform used to drill the well Parent Role The intention of this attribute is to track the reason why a child borehole was created within its parent. The current data has the following values: REDRILL: RESPUD: SIDETRACK: <Blank>: Well does not match one of the other values Primary Target This attribute is a free form text specifying the short code the operator employed to identify the intended target of the wellbore. 19

22 2.3.6 Other Class In an older version of the system there was an attribute called class that controlled how the well was drawn on a map. It was decided that this should be split into Flow Class which notes the fluids associated with a well and Other Class that holds additional information. The values used here are: JW: Junked Well DR: Drilling OBSW: Observation RW: Relief Well S: Suspended above TD WDW: Water Disposal Well Wellbore Path The wellbore path is often provided in detail by listing points along the path in a separate file. These usually take the form of an Azimuth survey (with values for MDKB, Drift Angle and Azimuth Angle at each point) or an Offset path (with values for MDKB, TVDSS, X Offset and Y Offset at each point). The Offset style is usually calculated from the Azimuth one by employing a minimum curvature algorithm. Because this is a distinct file it may be permitted to specify distances in metres or feet (International Feet unless the unit is fully specified). In any case it is important to specify the units being employed both for the distances and angles in the file. Whether the Azimuth angle is related to True North, Magnetic North or Grid North must be clearly stated. There is no support for this attribute in the current tool. In future versions this may be added. 20

23 3 Quality Tests This section will list textual descriptions of the various tests to be carried out on the wellbore data. # Description Dimension Quality of 1 Must have valid COUNTRYCOD Consistent COUNTRYCOD 2 Must have valid QUADRANT Consistent QUADRANTNO 3 BLOCKNO must be 2 digits Reasonable BLOCKNO 4 BLOCKSUFFI must be single lower case letter Consistent BLOCKSUFFI 5 PLATFORM must be single upper case letter or Consistent PLATFORM empty 6 DRILLSEQNO integer value > 0 Consistent DRILLSEQNO 7 WELLSUFFIX must be single upper case letter or Consistent WELLSUFFIX empty 8 DENNO must be a integer > 0 if the well is offshore Consistent DENNO 9 RESPONSIBLE_COMPANY must be valid Consistent RESPONSIBLE_ company group COMPANY 10 FIELD is either the string NOT IN FIELD or a Consistent FIELD valid field name 11 TOPHOLEYDD is a number between 48 and 64 Reasonable TOPHOLEYDD 12 TOPHOLEXDD is a number between -26 and 4 Reasonable TOPHOLEXDD 13 TOPHOLEYDD matches the QUADRANT Consistent TOPHOLEYDD 14 TOPHOLEXDD matches the QUADRANT Consistent TOPHOLEXDD 15 TOPHOLEDTM is OSGB 1936 for land wells Consistent TOPHOLEDTM and ED 50 or ETRS89 for offshore wells 16 BOTHOLEDTM must match TOPHOLEDTM Consistent BOTHOLEDTM 17 BOTHOLEYDD is a number between 48 and 64 Reasonable BOTHOLEYDD 18 BOTHOLEXDD is a number between -26 and 4 Reasonable BOTHOLEXDD 19 BOTHOLEYDD matches the QUADRANT Consistent BOTHOLEYDD 20 BOTHOLEXDD matches the QUADRANT Consistent BOTHOLEXDD 21 Less than 30km distance from TOPHOLEYDD to Reasonable BOTHOLEYDD BOTHOLEYDD 22 Less than 30km distance from TOPHOLEXDD to Reasonable BOTHOLEXDD BOTHOLEXDD 23 DATUMTYPE is DF, RT or KB for offshore Consistent DATUMTYPE wells and AGL, GLE, DF, RT or KB for onshore ones 24 DATUMELEV must be number greater than 0 Consistent DATUMELEV 25 If DATUMTYPE is DF, RT, KB or AGL value Reasonable DATUMELEV should be below GROUNDELEV should be unset if the well is Consistent GROUNDELEV offshore 27 GROUNDELEV should be a number greater than Consistent GROUNDELEV 0 if the well is onshore 28 WATERDEPTH should be unset if the well is Consistent WATERDEPTH onshore 29 WATERDEPTH should be a number greater than 0 if the well is offshore Consistent WATERDEPTH 21

24 # Description Dimension Quality of 30 WATERDEPTH should not exceed 4000 Reasonable WATERDEPTH 31 TOTALMDDRI should be a number greater than Consistent TOTALMDDRI 0 32 TOTALMDDRI should be less than Reasonable TOTALMDDRI 33 TVDSSDRILL should be a number greater than 0 Consistent TVDSSDRILL 34 TVDSSDRILL should not be greater than Reasonable TVDSSDRILL (TOTALMDDRI DATUMELEV) 35 LICENCE_NUMBER is a valid licence Consistent LICENCE_NUM BER 36 OPERATOR is either empty string or valid Consistent OPERATOR COMPANY 37 The OPERATOR cannot be empty if the well Reasonable OPERATOR status (COMPLESTAT) is set to COMPLETED_OPERATING 38 ORIGINTENT must be A, E or D Consistent ORIGINTENT 39 COMPLESTAT must be valid _STATUS Consistent COMPLESTAT 40 If the COMPLESTAT is PLANNED then the Reasonable SPUDDATE SPUDDATE should be empty 41 If the COMPLESTAT is not PLANNED then Reasonable SPUDDATE the SPUDDATE should not be empty 42 If the SPUDDATE is not empty it should have a Reasonable SPUDDATE date after 1 Jan 1900 and before today 43 If the COMPLESTAT is PLANNED or Reasonable COMPLEDATE DRILLING then the COMPLEDATE should be empty 44 If the COMPLESTAT is neither PLANNED nor Reasonable COMPLEDATE DRILLING then the COMPLEDATE cannot be empty 45 If the COMPLEDATE is not empty it should have Reasonable COMPLEDATE a date after the SPUDDATE and before today 46 If the COMPLEDATE is not empty then the Reasonable DATETDREAC DATETDREAC should be between the SPUDDATE and COMPLEDATE 47 FLOWCLASS must be valid _FLOWCLASS Consistent FLOWCLASS 48 TOPHOLEYDD matches the BLOCK Consistent TOPHOLEYDD 49 TOPHOLEXDD matches the BLOCK Consistent TOPHOLEXDD 50 BOTHOLEYDD matches the BLOCK Consistent BOTHOLEYDD 51 BOTHOLEXDD matches the BLOCK Consistent BOTHOLEXDD 52 If the COMPLEDATE is not empty it should have a date less than a year after the SPUDDATE Reasonable COMPLEDATE 53 If the COMPLEDATE is not empty the Reasonable COMPLEDATE COMPLESTAT should not be PLANNED or DRILLING 54 The WATERDEPTH should not be less than the Reasonable WATERDEPTH QUADRANT s minimum (if defined) 55 The WATERDEPTH should not be greater than Reasonable WATERDEPTH the QUADRANT s maximum (if defined) 56 The WELL_ORIGIN must be populated with a Consistent WELL_ORIGIN valid wellbore name 57 The WELL_ORIGIN should be in the currently considered set of wellbores Consistent WELL_ORIGIN 22

25 # Description Dimension Quality of 58 Where the WELLREGNO is the same as WELL_ORIGIN the WELLBORE_SEQUENCE Reasonable WELLBORE_ SEQUENCE should be WB1 59 When the WELLBORE_SEQUENCE is not WB1 the WELL_ORIGIN should be different Reasonable WELL_ORIGIN from the WELLREGNO 60 Where the WELLREGNO is not the same as WELL_ORIGIN the WELLBORE_SEQUENCE should not be WB1 61 The WELLBORE_SEQUENCE contains the text sequence "WB" followed by a positive integer 62 A development well must be associated with a real field (i.e. the FIELD value cannot be NOT IN FIELD ) 63 If the WELL_ORIGIN wellbore has a status of "AB3" then this wellbore must have a status of "AB3" 64 If the WELL_ORIGIN wellbore has a status that is not "AB3" then this wellbore cannot have a status of "AB3" 65 If the PLATFORM is defined the SLOTNO should not be empty 66 The WELL_ORIGIN wellbore should have a DRILLSEQNO that is less than or equal to this wellbore s DRILLSEQNO 67 The DRILLSEQNO should match the final number in the WELLREGNO 68 If the WELLSUFFIX is R or empty the WELLREGNO ends in a digit otherwise the WELLREGNO ends in the WELLSUFFIX 69 If the PLATFORM is not defined the SLOTNO should be empty Reasonable Consistent Consistent Consistent Consistent Consistent Consistent Consistent Consistent Consistent WELLBORE_ SEQUENCE WELLBORE_ SEQUENCE FIELD COMPLESTAT COMPLESTAT SLOTNO DRILLSEQNO DRILLSEQNO WELLSUFFIX SLOTNO 23

26 4 Wellbore Validation Tool The OGA has created a spreadsheet based tool to assist companies that are validating the wellbores. This will be provided to each company pre-populated with: the current data they are responsible for; software to carry out the tests; and some reports to illustrate progress. Figure 12: Report of data quality in the OGA wellbore validation tool In Figure 12 above, for example, the user can see which attributes have triggered most failures, which rules have detected most issues and some overall measures of data quality and failure rates. You should have been sent a version of this tool populated with just the wellbores that your company is responsible for. The goal here is to revise the data in the Wellbores tab so that it represents the correct values for all the wellbores. There are a number of tools and summaries to help you quickly identify issues. A simple example will show the way these tools can be used. If there are wellbores that you feel you have incorrectly been assigned responsibility for then you can edit their RESPONSIBLE_COMPANY attribute to suggest which company group they should be assigned to. Any wells where the RESPONSIBLE_COMPANY value does not match that shown on the Control tab will be greyed out and the attribute values will not be checked. If you elect to modify this attribute you must separately explain why these wells should be reassigned when you return the data to the OGA. The Control tab shows a number of displays that illustrate and track how the quality of the data is improving. The attributes that are the most frequent cause of failures are indicated with the red bars (in the case shown in Figure 12 the field name, bottom hole location and licence number all need to be addressed). The rules table shows, for example, that Rule 10 is triggered frequently, the quality rules (listed in Chapter starting on page 20) show that this is a rule related to field names. Pressing the ReDo Checks button will cause the tool to re-evaluate the current data and insert highlights and comments into the Wellbores tab. Cells in that tab that are coloured in red indicate 24

27 attributes that have failed some tests, cells may also be coloured to indicate warnings, where values that are apparently incorrect may be justified. Each coloured cell will also have a note attached to list the rules that it has triggered, these can be reviewed by hovering the mouse cursor over the cell. Figure 13: Two failures in the BOTHOLEXDD attribute The blue ellipse in Figure 13 above shows where a longitude value is positive (while the corresponding top hole location has a negative value). In addition the comment tells the user that the value of (which is not a severe error but is worth checking) has failed rules 20 and 51. Any of the cells in the Wellbores tab may be edited, so in the above case the value picked out by the blue ellipse may be changed from a clearly incorrect positive value to its inverse. This value may also be incorrect but it seems likely that a negative value of is going to be closer to the actual value than the current one is. Of course in a real situation this value would need to be obtained from other internal company systems or by examining the original drilling report. When the data values in the Wellbores tab have been updated then activating the ReDo Checks button will reprocess and highlight the current issues. After cycling through finding corrections, editing the data and redoing the checks the summary numbers on the Control tab will show the improvement to the quality that has resulted. At any time activating the Show Edits button (also on the Control tab) will remove the formatting that shows rule failures. The Wellbores tab will now highlight all the cells that have changed value since the data was originally sent. 25

28 Figure 14: The Show Edits button shows what has been changed In the illustration above all the cells with pale yellow backgrounds have been modified. This shows not only where the well datum type has been changed (to RT and KB ) but also where values of 0 in the ground elevation has been removed (being offshore wells a ground elevation of zero is somewhat unlikely). Once the data in the Wellbores tab has been edited to reflect your best understanding the spreadsheet should be returned to OGA together with a descriptive note that confirms values for: Your Company Group Name The name of the person in your organisation who has approved the values The position of that person The data on which the values were deemed correct A justification for any wellbores that should be assigned to a different company group If there are any questions about the use of this tool, suggestions for how it could be improved, or clarifications about the meanings of its terms then please contact OGA immediately, a list of names and contact details has been provided on page 2 of this document. 26

29 4.1 The Overall Process Figure 15: The overall process to correct the wellbore data The company updates are the most important step in an overall process to improve the quality of the wellbore data that OGA holds. The overall process consists of the following steps: Data Merge: obtaining the current OGA, CDA and other wellbore data and combining it Select Data: identifying the data that is the responsibility of a particular company and structuring it for correction Adjust Data: within each company check any data issues against internal data resources and correct the values Checking: once corrections are submitted to OGA they are checked to ensure the returned values are plausible Updating Data: the modifications are finally applied to the OGA data and distributed to other data sources If you want to discuss any of these other stages in the overall process please contact any of the OGA staff listed on page 2. 27

30 4.2 Control Tab Figure 16: Control tab in the wellbore quality checking tool The initial tab provides a summary of the data quality issues. In addition to the two action buttons that were explained in the previous section there are the following components: Action Buttons: these two button process the Wellbores tab, the first does a quality analysis, the second makes it easy to find values that have been modified locally Overall Score: gives a summary indication of the overall quality score for this data. If the data has no detected issues it would have a score equal to 100 Attribute Summary: provides an indicator for each attribute, the height of the red bars shows the proportion of the wellbores that have issues detected for each attribute Attribute Rates: shows the proportion of all attributes that failed or passed the tests Wellbore Issues: shows the proportion of wellbores that had no issues, those with a single attribute that failed and so on Rule Summary: shows the rates at which each rule failed Wellbore Issues: shows a graphical version of the wellbore issues data, the count of wellbores which have no issues, just one failing attribute and so on Original Attributes: provides the same type of display as the Attribute Summary but using the original data. This is for comparison purposes against the current state Rebuild Tests: certain operations of the Wellbores worksheet may disrupt the rule tests (on the Tests worksheet). This button will rebuild the rules 28

31 4.2.1 Overall Score The overall score provides a headline measure of the overall data quality. It is based on estimating the average number of attributes with issues for each wellbore. The exact calculation is: (average number of attribute failures) 100*0.7 In a sense this can be seen as an arbitrary measure but it does allow a direct comparison of one set of wellbore data with another and it provides an obvious indication of the impact that different data corrections has. The metric is also deliberately structured to emphasise the impact of the type of improvement gained when the data is approaching perfection. At that stage corrections are harder to identify and they each impact fewer entities. In other words it is a better match for the effort required rather than just the number of entities impacted. This metric has the advantage that it does not depend on the absolute number of wells involved (so can be used to compare well sets with radically different sizes). However it does depend on the exact set of rules employed, each additional rule can only decrease the metric. This means that when expressing this as a number one should strictly specify which rule set it is measured against. In practice those that want to see a simple summary number usually don t want to be exposed to the complexities of how it is reached. A number of different parameters were tried and these were chosen as the best reflection of previous experience in data quality improvement projects. 4.3 Wellbores Tab The second tab in the spreadsheet holds the current state of the wellbore data. Each row represents a different wellbore, the columns showing the values of the attributes. This tab can be in one of two modes. In results mode the majority of cells will have a pale yellow background, other colours indicate cells that have triggered one or more quality rules: Red Cells: indicate values that need to be corrected (failed rules) Pink Cells: indicate values that are almost certainly wrong but possibly may be valid (warned rules) Orange Cells: indicate values that should be carefully checked, since they seem to be invalid but may possibly be justified (noted rules) In edit mode the majority of cells will have white backgrounds and pale grey text, any cell whose value has been modified will have a yellow background and black text. This allows the user (and OGA) to quickly identify the fixes that have been applied to the data Identifying wellbores with particular combinations of issues One of the most frequent requirements is to focus only on wellbores that match a combined set of conditions. Unfortunately there are too many potential combinations to easily build this type of capability into the existing tool; however it is quite easy to exploit Excel s capabilities to achieve this type of result. 29

32 For example suppose we wanted to identify only the wellbores that passed Rule 29 but failed Rule 54. There are clearly a number of ways to do this employing Excel s inbuilt facilities, here is one method: In the Wellbores tab find an unused column such as AS Into the first wellbore cell in that column (cell AS2 ) enter the Excel formula =AND(OFFSET(Tests!$A$1,ROW()-1,29)=0, OFFSET(Tests!$A$1,ROW()-1,54)=9) Duplicate the AS2 cell to all the wellbore rows (a range like AS3:AS450 ) Select the AS column and filter on it (in the Data tab select the Filter command) Select just the cells with a value of TRUE Now only the wells that match the criteria will be shown. The fact that additional data has been entered to the Wellbores tab will not cause any issues provided it is inserted beyond the range supplied (in version that would be beyond the AS column). This relies on the fact that the Tests tab has a cell for each test carried out on each wellbore. When tests pass these cells have a value of 0, when they fail the cell will have a value of 9, or an error state indicating the type of issue that was encountered. 4.4 Original Data Tab This tab contains a record of the wellbore data before any fixes were applied. The contents of this tab should not be modified at all. Figure 17: The Original data shows the values originally supplied This tab is colour coded to allow the user to see where this data originated from. Most of the data was extracted from the OGA dataset and this is indicated by the cells with light blue text. A number of the values were subsequently overwritten by those coming from CDA; these have been indicated using the CDA colours (orange with dark blue text). 4.5 Rules Tab This tab contains a list of the quality rules (and a summary of the results of applying them). The rules listed here should be the same as those in Chapter of this document. 30